No abstract

We report the isolation and sequencing of genomic copies of mariner transposons involved in recent horizontal transfers into the genomes of the European earwig, Forficula auricularia; the European honey bee, Apis mellifera; the Mediterranean fruit fly, Ceratitis capitata; and a blister beetle, Epicauta funebris, insects from four different orders. These elements are in the mellifera subfamily and are the second documented example of full-length mariner elements involved in this kind of phenomenon. We applied maximum likelihood methods to the coding sequences and determined that the copies in each genome were evolving neutrally, whereas reconstructed ancestral coding sequences appeared to be under selection, which strengthens our previous hypothesis that the primary selective constraint on mariner sequence evolution is the act of horizontal transfer between genomes.

The amphipod Hyalella azteca is commonly used as a model for determining safe concentrations of contaminants in freshwaters. The authors sequenced the mitochondrial cytochrome c oxidase subunit I (COI) gene for representatives of 38 populations of this species complex from US and Canadian toxicology research laboratories and eastern North American field sites to determine their genetic relationships. With 1 exception, all US and Canadian laboratory cultures sampled were identified as conspecific. In 22 wild populations spanning 5 US states and 1 Canadian province, the commonly occurring laboratory species was found only in northern Florida, USA. Therefore, the diversity of the H. azteca species complex detected in the wild is not accurately represented in North American laboratories, questioning the reliability of H. azteca cultures currently in use to accurately predict the responses of wild populations in ecotoxicological assays. The authors also examined the utility of different COI nucleotide fragments presently in use to determine phylogenetic relationships in this group and concluded that saturation in DNA sequences leads to inconsistent relationships between clades. Amino acid sequences for COI were not saturated and may allow a more accurate phylogeny estimate. Hyalella azteca is crucial for developing water-quality regulations; therefore, laboratories should know and standardize the strain(s) they use to confidently compare toxicity tests across laboratories and determine whether they are an appropriate surrogate for their regions.

Evaluating species boundaries remains a significant challenge in rare, difficult to collect, and/or understudied groups because of a lack of available data. Uninformative morphology, unknown ecologies and/or geographical distributions, inadequate comparative sequence data, and limited sample sizes present substantial challenges when applying commonly used methods for species delimitation. Here we present an approach that overcomes the challenges previously mentioned by integrating phylogeny, genetic distances, and a fixed diagnostic character (i.e. colour pattern) into the species delimitation process. The genus Entomobrya (Collembola) includes many species marked by complex and variable colour patterns. Many Entomobrya species have been named based exclusively on colour pattern, but the value of this character as a species-level diagnostic marker has been challenged. To test the hypothesis that colour forms in Entomobrya represent independent evolutionary lineages, i.e. distinct species, we used phylogenetic methods to evaluate the association between colour pattern and molecular variation in the cytochrome c oxidase I gene (COI) in 11 species of North American Entomobrya. The comparative analysis focused on 13 colour forms distributed amongst the species Entomobrya assuta, Entomobrya clitellaria, Entomobrya ligata, and Entomobrya quadrilineata. Phylogenetic analysis and genetic divergences sorted the 13 colour forms into seven independent evolutionary lineages, including three morphologically cryptic lineages diagnosable by colour pattern. However, genetic divergence did not always correlate with colour pattern variation, indicating that the diagnostic utility of colour pattern is species dependent and requires individual evaluation for each species. We propose that incorporation of the explicit species delimitation criteria developed for this study will result in a substantial advance in the identification and description of species in understudied taxa.

X-ray diffraction of the indirect flight muscle (IFM) in living Drosophila at rest and electron microscopy of intact and glycerinated IFM was used to compare the effects of mutations in the regulatory light chain (RLC) on sarcomeric structure. Truncation of the RLC N-terminal extension (Dmlc2 Δ2-46 ) or disruption of the phosphorylation sites by substituting alanines (Dmlc2 S66A, S67A ) decreased the equatorial intensity ratio (I 20 /I 10 ), indicating decreased myosin mass associated with the thin filaments. Phosphorylation site disruption (Dmlc2 S66A, S67A ), but not N-terminal extension truncation (Dmlc2 Δ2-46 ), decreased the 14.5 nm reflection intensity, indicating a spread of the axial distribution of the myosin heads. The arrangement of thick filaments and myosin heads in electron micrographs of the phosphorylation mutant (Dmlc2 S66A, S67A ) appeared normal in the relaxed and rigor states, but when calcium activated, fewer myosin heads formed cross-bridges. In transgenic flies with both alterations to the RLC (Dmlc2 Δ2-46; S66A, S67A ), the effects of the dual mutation were additive. The results suggest that the RLC N-terminal extension serves as a "tether" to help preposition the myosin heads for attachment to actin, while phosphorylation of the RLC promotes head orientations that allow optimal interactions with the thin filament.